Cathode-ray tube amplifier



June 7, 1949.

P. J. SELGIN 2,472,779

CATHODE-RAY TUBE AMPLIFIER Filed Feb. 17, 1947 SIGNAL SOURCE FIG.3

UTILIZATION CIRCUIT INVENTOR PAUL J. SELGIN WTORHEY Patented June 7, 949

UNITED STATES PATENT OFFICE CATHODE-RAY TUBE AMPLIFIER ApplicationFebruary 17, 1947, Serial No. 729,022

3 Claims.

This invention relates to amplifiers and particularly to multistageamplifiers of the type wherein a plurality of amplifying stages are connected efi'ectively in cascade.

In signaling systems there are numerous cases where signal amplificationmust be efiected by employing a plurality of amplifying stages, de-

spite the fact that amplifier tubes capable of high gain oramplification have been made available. It is customary to couple anumber of amplifying stages in cascade for the purpose of effecting asignal amplification having an order of magnitude approximately equal tothe product of the individual amplifications capable of being effectedin all of the stages. Usually grid-controlled vacuum tubes are employedin the various stages. The signal to be amplified is impressed upon thecontrol circuit of the first stage and the amplified signal effectsderived from the plate circuit. The amplified signal effects then areimpressed by suitable coupling facilities upon the control grid circuitof the succeeding stage. The other cascaded amplifier stages are coupledtogether in a similar manner. The signal amplification is accomplishedby conducting current through the tube and a load impedance device froma suitable source of current. For satisfactory operation most vacuumtubes require the impression upon the anode circuits of a voltage of fewhundred volts, which is the voltage of the current source.

Where the signals to be amplified are of the alternating type, any typeof coupling between the amplifier stages may be used. Preferably,however, the coupling usually is either capacitive or inductive. Byreason of this preferred type of coupling, the control grid circuits ofall of the amplifier stages may be operated at relatively low voltagesrelative to ground at which potential the cathode circuits of the tubesusually are operated. However, where the signals to be amplified are ofrelatively low frequency, commonly considered as direct current signals,inductive or capacitive couplings between stages are unsatisfactory forthe reason that the relatively low frequency signals are not readilytransmitted by such couplings. It, therefore, becomes necessary toemploy direct, or conductive, couplings between the amplifier stages inorder to pass the direct current signals. The vacuum tubes of thevarious stages of adirect current amplifier requirethe same voltages tobe impressed between the'respective anodes and cathodes thereof. As aresult, the control grid circuits of each of the cascaded amplifierstages, in addition to the first,

must be operated at increasingly higher voltages. Also, to maintain theproper anode-to-cathode voltage of these stages, the voltage of thespace current supply therefor must be made increasingly greater. If aconsiderable number of such amplifier stages are required, there must beprovided a space current source which is capable of furnishing voltagesextending sometimes to several thousand volts.

It is an object of the present invention, therefore, to provide amultistage amplifier capable of operating with the various stagescoupled to one another in cascade without the necessity of employingabnormally high operating voltages.

Another object of the invention is to provide a multistage signalamplifier, the various stages of which may be directly coupled incascade and the input and output circuits of all of these stages beingsusceptible of operation at substantially the same potential.

Still another object of the invention is to provide a novel cathode raydeflection tube having a plurality of stages in each of which anelectron beam is deflected and in which the output circuit electrodes ofone stage may be directly coupled to the input circuit electrodes of asucceeding stage for energization purposes.

A further object of the invention is to provide a novel cathode ray tubeof the deflection type wherein a plurality of electron beams areindividually deflected over respective target electrodes and in whichthe target electrodes of one stage are directly coupled by a novelstructure, providing a load circuit, to the deflecting electrodes of asucceeding stage.

In accordance with this invention there is provided a multistage signalamplifier of which each stage consists of a cathode ray deflectiondevice. In this type of amplifier, advantage is taken of the fact thatonce an electron beam is given the required acceleration to project itagainst a target electrode, the means for deflecting the beam over thetarget electrode may be operated at approximately the same averagevoltage as the average voltage impressed upon the target electrode. Insuch a case the average voltage impressed upon the deflecting and targetelectrode systems may be no greater than the voltage required to eifectthe desired acceleration of the beam. Accordingly, the number of suchstages may be coupled together in cascade by a direct connection of thetarget electrode of one stage to the deflecting electrodes of asucceeding stage. In this manner the electron beams of the succeedingstages may be deflected by systems which are energized from the targetelectrode system of a preceding stage. The signals to be amplified aredirectly coupled to the deflecting electrodes of the first stage and theamplified signals are derived from the target electrodes of the lastamplifier stage. As many stages of amplification as required may becoupled together in cascade in the manner described without thenecessity of progressively increasing the voltages required foroperation of the amplifier.

Further, in accordance with the invention, all of the amplifying stagesmay be incorporated in a single evacuated envelope. The various stagesmay be separated from one another by suitable shielding barrier plates.Each stage includes an electrode structure for producing an electronbeam, a target electrode system for the beam and a deflecting system fordeflecting the beam over the target electrode.

In a preferred form of the invention, the target -electrode systemconsists of a pair of electrodes symmetrically located relative to theundeflected path of the beam and the deflecting system consists of apair of plate electrodes suitably located on opposite sides of the beamto produce the required electrostatic deflecting field. The targetelectrodes of one stage are coupled to the deflecting electrodes of asucceeding stage by means of a pair of conductors terminatingrespectively at the target electrodes and the deflecting electrodes.These conductors are carried through the barrier plate between the twostages. For this purpose the plate is provided with two openings, ineach of which is inserted a lead-through bushing in the form of carbonparticles suitably held together by a binding material. The conductorsare inserted in holes formed substantially through the centers of thelead-through bushings. In this manner the bushings provide a resistiveconnection between the coupling conductors and the barrier plate whichmay be connected to a source of voltage. The lead-through bushingscomprise a load for the target electrodes so that signal representativevoltages may be developed at the target electrodes in accordance withthe magnitude of the beam deflection. This voltage thus provides thedeflecting voltage for the succeeding stage. If desired, the signalvoltage may be impressed upon the first pair of deflecting electrodesand the amplified signal voltage may be derived from the last pair oftarget electrodes in a similar manner utilizing resistive lead-throughbushings.

For a better understanding of the invention, together with other andfurther objects thereof, reference is made to the following description,taken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

In the accompanying drawing:

Fig. 1 is an elevational view, partly in section, of a cathode ray tubeembodying the invention as a four stage amplifier;

Fig. 2 is a transverse sectional view of the tube taken on the line 22of Fig. 1, and;

Fig. 3 is a schematic representation of a four stage cathode ray tubeamplifier illustrating the coupling between stages, the input and outputcircuits and the auxiliary power supply connection for the device.

Having reference now particularly to Figs. 1 and 2 of the drawing, thestructure of the cathode ray tube consists of an evacuated envelopewithin which are mounted the tube electrodes forming the four stageamplifier. Thetu-be is separated generally into four substantially equalhorizontal compartments by means of five metallic barrier plates l2, I3,l4, l5 and IS. The electron beams for all of the amplifier stages areformed from the electron emission produced by an elongated cathode I!which extends vertically through suitable openings formed in all of thebarrier plates. Within each of the compartments formed by these plates,the electron emission from the cathode is partially focused into anelectron beam by means of electron repelling electrodes l8, 19, 2| and22, respectively. The cathode l1 and the repelling electrodes are allelectrically insulated from the barrier plates and from one another. Theelectron emission in the various compartments of the tube is acceleratedand completely focused into a beam by accelerating electrodes 23, 24, 25and 26, respectively, located in front of the cathode. Theseaccelerating anodes each are provided with small apertures such as theaperture 21 of the anode 24 (shown in Fig. 2'). In front of the anodesin each of the tube compartments there are located four pairs ofdeflecting electrodes 28, 29, 3| and 32, respectively. At the other endof the compartments target electrodes 33, 34, and 38 respectively aremounted substantially at right angles to the path of the electron beam.If desired, there may be located between the electrodes of each pair oftarget electrodes a secondary electron emission inhibiting electrodesuch as 31, 38, 39 and 4|, respectively.

The first stage pair of target electrodes 33 are connected respectivelyby a, pair of conductors 42 to the deflecting plates 29 of the secondstage. These conductors are imbedded in beads or leadthrough bushings 43which are mounted in suitable holes in the barrier plate I3. Theseleadthrough bushings may be of substantially any desired type havingresistance between the embedded conductors and the plate in which theyare mounted. Finely granulated particles of carbon, held together by anywell known binder, are suitable for the bushings. In like manner thetarget electrodes 34 are connected by a pair of conductors 44 throughresistive lead-through bushings 45 to the third stage deflectingelectrodes 3|. Also, the third stage target electrodes 35 are connectedby a ,pair of conductors 45 through resistive lead-through bushings 4]to the fourth stage deflecting electrodes 32.

The first stage deflecting electrodes 28 are energized by the impressionthereon of a signal voltage. This may be accomplished by connecting tothese electrodes a pair of conductors 48 which may be supported in thebarrier plate 12 by lead-through resistive bushings 49. In like mannerthe target electrodes 35 of the fourth stage may be connected by a pairof conductors 5| which are suppported in lead-through resistive bushings52 in the barrier plate IE to the output circuit.

The cathode I! may be heated either directly or indirectly in any mannerknown to those versed in the art, by suitably connecting conductors 53and 54 to a suitable power supply. In order that the cathode may be madea unipotential device, it is preferable to employ indirect heatingthereof. The conductor 54 may be grounded so that the secondary electronemission inhibiting plates '31, 38, 39 and 4| may be connected thereto.The repelling electrodes 8, l9, 2| and 22 may be connected by aconductor 55 to a source of voltage which is of negative polarity withrespect to'the cathode voltage. 'The barrier plates l2, l3, l4, l andIS, the accelerating anodes 23, 24, 25 and 26 may be connected by aconductor 56 to a source of voltage which is of positive polarityrelative to the cathode voltage.

Referring now to Fig. 3 of the drawing, there is shown the tube elementsand associated circuit components in diagrammatic form. It will beunderstood that, while the cathode I1 is shown broken up among thevarious tube stages, the actual physical structure of the cathode is asdescribed in conjunction with Fig. 1. Also, the resistive lead-throughbushings for the coupling conductors between amplifying stages and tothe external circuits are illustrated in Fig. 3 by conventionaldiagrammatic circuit symbols. The various tube electrodes are providedwith suitable operating potentials by means of connections to a powersupply such as shown herein by a battery 5?. The negative terminal ofthe battery is connected by the lead-in conductor 55 to the electronrepelling electrodes I8, l9, 2| and 22 of the four amplifying stages. Asomewhat more positive point of the battery is connected to the cathodeH by means of the lead-in conductor 53. Also in this form of theinvention the cathode is connected to ground by means of the conductor54. Alternatively, instead of grounding the oathode the conductor 55 maybe grounnded and, in that manner, the input and output circuits of theamplifier may be operated substantially at ground potential. Inaddition, the secondary electron emission inhibiting electrodes 31, 38,39 and 4! are shown connected to ground by the conductor 54. Thepositive terminal of the battery 5'! is connected by the lead-inconductor 56 to the interstage barrier plates l2, l3, l4, l5 and It andalso to the accelerating anodes 23, 24, 25 and 25.

A signal source 58 is shown connected by leadin conductors 38 to theterminals of the resistive bushings 49 and also to the first stagedeflecting electrodes 28. The last stage target electrodes 36 are shownconnected to the terminals of the resistive bushings 52 and also to autilization apparatus or circuit 59 by means of the pair of lead-inconductors 5|.

Referring now to the operation of the device, it will be understood thatin each of the four amplifying stages shown, there is produced anelectron beam. In the first stage, for example, the electron emissionfrom the cathode I1 is formed into a beam by means of the repellingelectrode 18 and the accelerating anode 23. The beam passes between thedeflecting electrodes 28 and is directed against the target electrodes33. A signal voltage which is derived from the source 58 is impressedupon the resistive lead-through bushings d9. Effectively, the signalvoltage is connected to the terminals of these two resistive units whichare connected electrically in series. By reason of the structuralarrangement of these resistive units, relative to the barrier plate I2,the efiective midpoint of the series circuit is coupled to the positiveterminal of the battery 57. Thus, the average unidirectional voltage ofthe deflecting electrodes 28 is substantially equal to the potential ofthe positive battery terminal. The instantaneous voltages of the twodeflecting electrodes varies in accordance with the impressed signal.Depending upon the instantaneous voltages impressed upon the deflectingelectrodes 28, the electron beam of the first stage is deflected overthe target electrodes 33. An upward deflection of the beam, for example,causes the impingement of more electrons on the upper electrode andfewer electrons upon the lower target electrode.

The connections of the target electrodes 33 by the conductors 42 to theresistive units 43 and the connection of these resistive units to thebarrier plate is and hence to the positive terminal of the battery 5!impresses an average unidirectional voltage upon the target electrodes33 which is substantially equal to the potential of the positive batteryterminal. The variation of the respective numbers of electrons impingingupon the upper and lower target electrodes 33 as a result of thedescribed beam deflection, develops instantaneous voltages across theresistive units 43 in accordance with the electron impingement of thetarget electrodes.

The varying voltages developed in the resistive units 43 are impressedupon the deflecting electrodes '29 of the second amplifying stage. Thesevoltages, in general, are of greater magnitudes than the signal voltagesimpressed upon the first stage deflecting electrodes 28 by reason of theamplifying characteristic of the first stage, Consequently, thedeflection of the electron beam of the second stage will be greater thanthe defiection of the first stage beam. The voltage variations also willbe in accordance with the signals derived from the source 58. Under theinfluence of these increased voltages, the electron beam of the secondstage will cause a greater variation in the numbers of electronsimpinging upon the target electrodes 35. The signal representativevoltages developed in the resistive units 45 as a result will be ofgreater magnitudes than those developed in the output circuit of thefirst stage. The impression of these amplified signal voltages upon thedeflecting electrodes 3! of the third stage causes a still greaterdeflection of the beam of this stage over the target electrodes 35 andan even greater signal representative voltage thus is developed in theresistive units 41 for impression upon the deflecting electrodes 32 ofthe fourth and final stage. A maximum deflection of the electron beam ofthe last stage is, therefore, effected over the target electrodes 36.Accordingly, the signal representative voltage developed in the outputcircuit resistive units 52 is of a considerably increased magnitude,relative to the signal voltage derived from the source 58. The magnifiedsignal voltage developed in the resistive units 52 is impressed upon theutilization circuit 59.

It is seen that, by virtue of the novel structure of the cathode raytube and the circuit arrangement of its components, the input circuitsof all of the amplifier stages and the output circuits thereof may beoperated at substantially the same average unidirectional voltage. It,therefore, is necessary to provide a power supply for the operation ofsuch a device which is required to have no greater voltage outputcapacity than is required for the operation of a single stage. In thismanner many of the difficulties encountered in operating multistagedirect current amplifiers are avoided. Also, a device of the characterdescribed is susceptible of such construction that a number ofamplifying stages may be included in a single envelope as illustratedand described herein. In such a case there are required no more lead-inconductors to the device than are required for the operation of a singleamplifying stage. This simplifies the manufacture of such a device. Alsothere is effected the advantage of minimizing capacity betweenconact/awe ductors and between the conductors and ground. This sameadvantage is also secured by the relative simplicity of the tubestructure wherein the number of components is maintained at a minimum.Obviously, the invention is not limited to the use of the specific typeof lead-through bushings disclosed herein. Other types of coupling andload resistors are contemplated as coming within the purview of theinvention. For example, conventional resistor units, mounted eitherinternally or externally of the tube may be used without departing fromthe invention.

Furthermore, it is not necessary, in order to practice the invention, tohave all of the amplifier stages in the one envelope. Groups of stagesmay be provided with separate envelopes or, i'fdes'ired, each stage maybe contained within an individual envelope.

While there has been described what is cousincred, at present, thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is aimed,therefore, in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

'1. A cathode ray tube comprising, an evacuated envelope, means forproducing a plurality of electron beams, a pair of deflecting plates anda pair of target electrodes for each of said beams, a plurality of pairsof resistors mounted in said envelope, there being one pair of saidresistors for each of said beams, and conductors coupling respectivepairs of said resistors to the target electrodes for one of said beamsand to the deflecting electrodes for another one of said beams.

2. A cathode ray tube comprising, an evacuated envelope, a plurality ofspaced parallel plates mounted in said-envelope and dividing said tubeinto apluralityrof compartments, an electron gun, apair of deflectingelectrodes and a pair of target electrodes in each of said compartments,a pair of resistive bushings mounted in openings in each of said Platesand in good electrical contact with said plates, and conductorsextending through said bushings and in good electrical contact therewithconnecting the respective target electrodes of one compartment to thedeflecting electrodes of an adjacent compartment.

3. A cathode ray tube comprising, means for producing a plurality ofparallel electron beams, a plurality of barrier plates located betweensaid beams and dividing said tube into a plurality of compartmentsonefor each of said beams, a pair ordefiecting plates and a pair of targetelectrodes located respectively in each of said compartments, meansincluding resistive bushings mounted in said barrier plates for couplingrespectively the target electrodes of each of said stages, except thelastto the deflecting electrodes of all of said stages, except thefirst, means for energizing the deflecting electrodes of said firststage according to signal effects and means for deriving from the targetelectrodes-of said last stage amplified signal elfects.

PAUL J. SELGIN.

REFERENCES CITED The following referen ces are of record in the file ofthis patent:

UNIT-ED STATES PATENTS Number Name Date 1,990,733 Helntz Feb. 12, 19352,064,469 'Haeff Dec. 15, 1936 2,205,071 Skellett June 18, 19402,214,729 Hickok Sept. 17, 1940 2,262,406 Rath Nov. 11, 1941

